X-ray imaging can be a useful medical diagnostic tool. In mammography, for example, X-rays are used in an attempt to detect cancerous tissue at the earliest possible growth stage. If identified sufficiently early, such tissue can be treated or surgically removed, improving the patient's prospects for long term survival.
Unfortunately existing mammography X-ray imaging cannot detect small cancerous tissue and microcalcifications that may be an indication of malignancy until they are sufficiently large to register upon the X-ray film. In practice, existing mammography imaging systems use X-ray dosages of about 100 millirad to the X-rayed tissue, but cannot reliably detect microcalcifications smaller than about 200 .mu.m (0.20 mm).
The first art X-ray systems exhibited poor sensitivity, due to loss of useful X-rays in reaching the X-ray film, and due to the low sensitivity of the X-ray film itself. In practice, a scintillation screen is placed atop the X-ray film such that impinging X-rays cause the scintillation screen to flash, exposing the underlying X-ray film. The scintillation screen must be thick enough to stop all incoming X-rays, but unfortunately the flashed light spreads out within the thickness of the scintillation screen enroute to the underlying film. Thus, while the scintillation screen/film combination enhances detection sensitivity compared to using the X-ray film alone, detection of small sized particles in impaired because of the scintillation screen thickness.
In short, although microcalcifications smaller than 0.2 mm may indicate the presence of breast cancer, such small targets cannot be detected with existing X-ray systems.
FIG. 1 depicts a conventional X-ray imaging system wherein a stationary X-ray source 2 emits X-rays 4 that pass through an opening 6 in a stationary upper collimator 8 that limits the radiation field to the size of the patient object 10 under examination. Object 10 may include a tissue region 12 possible including microcalcifications, whose presence is sought to be detected with the X-ray system.
Radiation passing through upper collimator 8 includes X-rays 14 that scatter due to the Compton effect, and direct X-rays 16. Although it would be beneficial to detect and thus use all of the X-rays that have irradiated object or patient 10, the prior art normally uses a lower collimator 18 to prevent the scattered X-rays from reaching the scintillation screen/film detector 20 located below the lower collimator. Lower collimators 18 such as shown in FIG. 1 are commonly called Bucky units.
As a result, only direct X-rays passing through narrow lower collimator openings or slits 22 without being absorbed are detected by the stationary detection medium 20. Stated differently, the prior art's reliance upon lower collimator 18 means that many X-rays that have irradiated the patient, that have not scattered and thus carry useful information, will be absorbed by the lower collimator 18 rather than pass through the lower collimator openings 22 to be detected. Some prior art systems may in fact can detect only about half of the X-rays exiting the subject 10.
This inability to detect all of the X-rays irradiating the patient contributes to lowered sensitivity for prior art systems. For example, a sufficiently small tumor or microcalcification within a tumor 12 in the object 10 may go undetected, notwithstanding that it may be cancerous. Although substantial, but relatively safe, levels of X-ray radiation are used in prior art systems to compensate for absorption in the lower collimator, nonetheless considerably more X-rays are needed.
Further, it will be appreciated that prior art detecting media, e.g., scintillating screen/film 20, in addition to degrading resolution sensitivity for tiny targets, provide an integration function. Essentially, direct X-rays that pass through openings in the lower collimator are integrated over time. There is no ability to distinguish X-rays arriving at one angle or at one time from X-rays arriving at a second angle or at a second time. Such ability would permit suspicious appearing targets 12 to be imaged from several angles, to provide an image locating the target in three-dimension breast space. A target that is not visible at one angle may in fact be visible when imaged at a different angle. Because of the integrating nature of prior art detecting media, three-dimensional imaging is barely feasible in the prior art. At best, two separate X-ray exposures are made at slightly different angles, and the two resulting X-ray films are superimposed and matched stereoscopically by hand. Needless to say, such manual matching does not permit computer analysis of the detected image, which analysis might readily detect suspicious targets likely to be missed by the human eye.
An additional limitation of prior art detection media 20 is that it is difficult to readily transmit copies of the detected image to remote locations. For example, a physician in a remote area might wish to consult with a specialist thousands of miles away with regard to a suspicious mammogram. In the prior art, the X-ray film is mailed to the specialist, or a copy made (with resultant image degradation) and mailed. At best, it will take hours or days before the specialist receives the image and can render an opinion to the examining physician. Although high resolution equipment that can scan an X-ray film and transmit the scanned data is being developed, such scanning equipment is relatively expensive and not readily available to many medical practitioners, especially practitioners in poorer countries.
In summary, there is a need for an X-ray system that can provide enhanced X-ray sensitivity, enhanced small target resolution, and preferably is filmless. Such system preferably would provide a detected image that can be electronically copied, stored, and/or transmitted rapidly over great distances. Further, there is a need for an X-ray system that, in addition to having the above advantages, can also provide three-dimensional imaging.
The present invention discloses such a system, and a method for implementing its use.